x = randint (1,900000);
z = 2 * x - 1;
n = randn(1, 900000);
for a=0:.1:10,
i = a /10;
s = sqrt(2*(10^i)).*z;
y = s + n;

t = sign (y);
%w = x ~= t;
%num = sum (w);
[x, ratio]=symerr (z, t); %num / 900000;
be(round(10*a+1))= ratio;
end
figure;
q=0:0.1:10;
i = 10 .^ (q / 10);
BER_theo = 0.5*erfc(sqrt(i));
semilogy (q, be,'--rs', q, BER_theo, 'c+:');
grid on,